I'm currently in a campaign th that started out as peaceful trading (until i got the skill to 300). In my experience, cavalry is MUCH better for a trade caravan. You spend most of the time on the road and cav is much faster than infantry even if you provide a horse for each of them. Cheapest solution is to travel aserai and vlandian lands. They both have elite cav that already starts as cav at tier 2, so they are actually cheaper than an infantry plus horse. If you see gallants (t3 version of the vlandian cav) in villages, they are even better. Upgrade from t2 to t3 uses a warhorse in their case, so the option of getting the t3 right away is a huge bargain since you don't have to provide a warhorse for that guy.
I find it a punish that as a faction leader I need to spend 100 hours grinding trade before I can buy and sell land. Feels like something a king should be able to do...
It doesn't take 100 hours to grind trade, but it does take a fair amount of time. There are ways to skip the grind, though: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-8KovOGWbc0c.html